I think Cinnamon is the best of bad options. The 1.2 release has made it a little better, but it still isn't great. I like having the ability to move the panel and make some other customizations, but it still isn't what I want.
Gnome-Shell's even worse. I may have ranted about it before, but I really (really, really, really) hate Gnome-Shell. I can't stand it. There's only one thing worse in my mind: KDE.
What a segue. Yeah, I've never been able to get used to KDE. Sure, it looks prettier than your openbox/fluxbox or lxde and even xfce, but I just can't get it. I don't know why, but KDE just isn't for me.
As for lxde, I think it's ugly. It probably works fine, but I think aesthetics play a huge role in what environment I'm going to use. Same for Xfce, it's functional, but I really don't like it (maybe if it were prettier, but that would make it less lightweight).
Unity's okay. It currently ranks behind Cinnamon and Gnome-Fallback. My only major gripe with it is the global menu. Other than that, it's fine.
I think the best setup I had was on Ubuntu 10.10 and 11.04, when Gnome2 was one of the either preinstalled or easily installed environments (the distro is really inconsequential in the setup, I just needed Gnome2). I had one panel, on the top. On that panel was the Mint Menu, which I still like, even in it's Gnome3 version, DocbarX for window management, which I still think it pretty nifty (I like how the Windows 7 taskbar works, the one icon for multiple windows is awesome, plus I don't really need the text next to it…), and the standard clock/notification/logout configuration.
I loved that setup. I like how Windows 7 manages windows (that's about the only thing I think Windows does better than everyone else).I wish that I could have that same setup now, just with Gnome3.
Gnome-Fallback's fine, it's just laking the ability to add Dockbar to it.
Okay, that should be it for at least six months…
Update (29 Dec 2012): My thoughts on the current versions of most DEs listed here have changed. I just don't feel the need to get rid of this post, for posterities sake.